This invention relates to subject matter disclosed in concurrently filed application Ser. No. 855,048, in the name of R. J. Kobayashi, et al.
This invention relates to auxiliary combustor systems for use with combustion engines. More specifically, this invention relates to an improved combustor system particularly for use with turbocharged reciprocating engines, and providing closely controlled combustor fuel flows at virtually all engine operating conditions.
Auxiliary combustor systems for use with combustion engines are well known in the prior art. Specifically, such combustor systems are provided with combustion engines such as a turbocharged diesel engine wherein the available energy level of engine exhaust gases at relatively low speed conditions is insufficient to drive the turbocharger to provide the desired turbocharger boost to maintain engine loadcarrying capacity. Accordingly, an auxiliary combustor is provided for supplementing the energy level of the exhaust gases supplied to the turbocharger at these relatively low speed conditions, and thereby supplementally drive the turbocharger to provide the desired boost pressure.
Prior art combustor systems have required a supply of fresh charge air to the combustor in order to obtain and maintain propagation of a combustor flame. In this regard, it has been common practice to provide bypass means for bypassing a portion of the compressed charge air from the turbocharger around the engine, and to conveniently position the combustor in the bypass means. Importantly, the turbocharger has been sized so that excess charge air is always available whereby fresh air is supplied to the combustor at all conditions of engine operation to maintain a combustor flame. See, for example, U.S. Pat. Nos. 3,048,005; 3,570,240; and 3,996,747. However, with these systems, inefficient quantities of fuel are burned in the combustor in order to maintain the desired high energy level of gases flowing through the combustor. Moreover, secondary ignition of fuel remnants in the engine exhaust gases is not possible.
Other prior art combustor systems have attempted to connect a combustor in series, or in-line, with exhaust gases exiting the engine. In this manner, the energy level of the exhaust gases is boosted for supplementally driving the turbocharger and remnants of unburned fuel in the exhaust gases are ignited to reduce system smoke and emissions. However, in the prior art, it has been found that the ignition and sustainment of a flame in the combustor is particularly difficult in the substantially vitiated exhaust gas atmosphere. Accordingly, prior art in-line combustor systems have also utilized atomization techniques in the combustor requiring the atomization of fuel with fresh charge air prior to any mixing with exhaust gases to maintain flame propagation. See, for example, U.S. Pat. Nos. 2,620,621; 2,633,698; 3,736,752; 3,849,988; 3,949,555; 3,988,984; 3,996,748; 4,004,414; 4,009,574; and 4,026,115. However, these systems are undesirable in that they too require an oversized turbocharger for providing fresh charge air to the combustor at all times to maintain the combustor flame. This continuous addition of charge air to the auxiliary combustor results in fuel-inefficient combustor operation, but has heretofore been necessitated by the inability of prior art systems to operate without fresh air.
Another problem in the design of prior art combustor systems has been to prevent gumming or coking of the fuel lines. That is, partial or complete gumming or coking of fuel in the fuel lines can adversely affect combustor performance. Such gumming and/or coking occurs rapidly in the high temperature exhaust gas environment, particularly when the combustor is shut down to leave fuel standing in the fuel lines. Some prior art systems have included purge apparatus intended to solve coking and gumming problems by coupling charge air for continuous passage through fuel lines. See, for example, U.S. Pat. No. 4,004,414. However, such apparatus is inoperable when the combustor and the engine are together shut down to eliminate charge air flow.
The combustor system of this invention overcomes the problems and disadvantages of the prior art by utilizing apparatus and methods for maintaining controlled fuel-efficient combustion in an in-line combustor without requiring the continuous addition of fresh charge air to the combustor. Moreover, the system of this invention provides improved means for closely controlling the fuel supply in response to engine operating conditions, and to automatically and positively purge fuel from the system upon combustor shutdown to prevent coking or gumming of fuel in the combustor.